Haven't read the thread yet, but I'm gonna answer the way I'm guessing a lot of folks have: It depends.
I bought an AR because I wanted one. I already had a 7.62X39 rifle in my Yugo SKS. I like it more than the AK's I've fired, so I saw no need for an AK.
If I was looking for a purpose, I'd have to weigh the options. for SHTF, AK is rugged and reliable, but not as accurate, and there isn't as big a domestic supply of ammo for it. The AR is more prone to trouble when dirty, but the US military uses 5.56, so there are many domestic sources to feed it. The conundrum is a gun that works is useless without ammo, and a gun that fails likely won't un-fail in the face of enormous supplies of gunny chow.